Rainfall during the first three years of the Land Retirement Demonstration Project was below average. In contrast, winter rainfall for the 2002-03 growing season was predicted to be fairly high (i.e., mild El Niņo conditions were predicted). In anticipation of these wetter conditions, an experiment-the Section 23 Restoration Trial-was developed in which various species could be evaluated during an above-average rainfall year. In this experiment, two species mixtures were compared. The first mixture, the "traditional mix" was composed of a subset (9 of 13) of the species that were imprinted on the HRS Plots. The second mixture, the "experimental mix" incorporated various species that had been used to some success in other restoration trials at Tranquillity, augmented by a few species that had demonstrated restoration potential elsewhere in California.
The Section 23 restoration trial occupied an area of approximately 28.3 ha (70 ac). This area had received some weed control and was the largest contiguous block of "unassigned" land remaining on the Tranquillity site. Plots were ca.3.0 ha (7.5 ac) in size; a complete randomized block design was applied, with treatments replicated four times. Micro-topographic contours (berms) were installed in all plots. Berms were aligned east to west and were the full length of the plot. Berm spacing was 30-ft, such that part of a flat and half of a berm would be imprinted in a single pass and with a final pass through the middle of a flat, there would be no overlap in seeding. In this manner, the berms were also compacted slightly. Berms were constructed on 11 December 2002. Imprinting was scheduled to follow immediately thereafter; however, rainfall during this period precluded the use of heavy equipment throughout December and imprinting was postponed until 28-31 January 2003.
Table 1. Species planted in the Section 23 Restoration Trial, including Family, common name, and seeding rate. Seeding rates are expressed in gross (i.e., not lbs. pure live seed) pounds per acre. Key to treatments: TRAD, Traditional; EXP, Experimental.
| Taxon | Family | Common Name | TRAD | EXP |
|---|---|---|---|---|
| Allenrolfea occidentalis | Chenopodiaceae | iodinebush | 9.4 | 9.4 |
| Aristida ternipes var. hamulosa | Poaceae | Spreading threeawn | - | 6.1 |
| Atriplex polycarpa | Chenopodiaceae | allscale saltbush | 10.3 | 4.7 |
| Bromus carinatus | Poaceae | California brome | 8.5 | - |
| Frankenia salina | Frankeniaceae | alkali heath | 6.2 | - |
| Gilia tricolor | Polemoniaceae | bird's-eye gilia | - | 20.5 |
| Grindelia camporum | Asteraceae | gumplant | - | 11.8 |
| Hemizonia pungens | Asteraceae | common spikeweed | 1.5 | 1.4 |
| Lasthenia californica | Asteraceae | California goldfields | 29.2 | 35.4 |
| Lupinus bicolor | Fabaceae | bicolored lupine | - | 3.4 |
| Nassella pulchra | Poaceae | purple needlegrass | - | 8.9 |
| Phacelia ciliata | Hydrophyllaceae | Great Valley phacelia | - | 1 |
| Sporobolus airoides | Poaceae | alkali sacaton | 15 | - |
| Suaeda moquinii | Chenopodiaceae | bush seepweed | 1.9 | - |
| Vulpia microstachys | Poaceae | small fescue | 18.2 | - |
Page created: March 1, 2005; Last updated: Dec. 20, 2005